For a considerable time now, military communications have been experiencing an unprecedented transformation. In principle, with the technology currently available in the civilian sector, any required information can be accessed from any position on the earth automatically and without human intervention, and any network subscriber can be contacted almost without time delay. The development of the internet is a qualitative and quantitative leap in communications, which was unimaginable even at the beginning of the 1990s. Using this type of communication for military purposes opens up completely new horizons.
Modern, network-centric warfare concepts make information available in an appropriate form and without time delay anywhere where it may be required. Communications systems appropriate for this purpose are already being intensively developed. Such systems are subject to extremely stringent requirements, for example, with regard to mobility, maximum inter-operability (also with civilian authorities (BOS)), transparency of the networks (wire-bound/wireless, PSTN, ISDN, LAN, WAN/radio/fixed-wireless networks, military/civilian), universal accessibility, transmission of information in the combination reconnaissance/navigation/impact: position report, presentation of position, friend/foe identification, sensor data, images from digital cameras, GPS tracking, e-mail, newsflashes, other IP services, spontaneous mobile networking (MANET) and independence from an infrastructure.
The type of communication used by tactical troops is changing at an increasing rate. Hitherto, the application “secure voice link”, that is to say, speech encoded and resistant to any possible interference, was the almost exclusive priority.
Nowadays, alongside radiotelephony, there is an increasing desire to link different communicating participants with person-to-person accessibility. This type of cross-linking to form systems demands interoperability of communications technologies and an integration of networks in combined systems.
For reasons of interoperability, the use of internet protocols, e.g. TCP/IP, is necessary for networking data communications. These protocols can be realized using narrowband radio technology, for example, with MIL-STD-188-220 B. This standard specifies the lower protocol levels for an interoperability of tactical radio appliances.
Tactical radio is currently based on channels with 25 kHz bandwidth, over which the conventional gross 16 kbit/s can be transmitted with FEC up to 9.6 kbit/s. The use of standard internet protocols for the realisation of spontaneous mobile networking (MANET) in military radio communications would be a rapid and cost favourable solution. However, this requires data rates within the range of Mbit/s and therefore bandwidths in the MHz range. Accordingly, these cannot be used in the radio channels with a bandwidth of only 25 kHz. In the tactical sector, up to company level, radio appliances with bandwidths within this range have, so far, not been used.
Radio appliances with fast data rates and the associated wide signal bandwidths are subject to the following restrictions with regard to the propagation of the radio signals along the surface of the earth (that is to say, without free-space propagation as in the case of airborne platforms): for effective use, a higher frequency range (225 MHz to 400 MHz, but also up to 2 GHz or above) is advisable. However, the range of radio signals decreases with increasing frequency. Increasing the power of transmission only increases this range to a moderate extent. Eight times the transmission power achieves only double the range.
The required bandwidth is proportional to the desired data rate. However, the range decreases with increasing bandwidth. As a result, if the data rate is increased from 16 kbit/s to 1.6 Mbit/s, the range declines by a factor of approximately 5. A further sacrifice with regard to range must be taken into consideration because wide bandwidths generally demand higher transmission frequencies—since the tactical frequency range from 30 MHz to 88 MHz can no longer be used because of the wide bandwidth and density of packing.
Higher-quality types of modulation require a larger noise margin and therefore achieve a lower range with the same transmission power by comparison with the use of simpler modulation methods. The number of radio appliances required for the necessary radio cover depends to a very considerable degree on the range.
DE 196 51 593 A1 and DE 198 07 931 relate to the optimization of these parameters.
Broadband radio appliances for fast data rates are certainly the ideal solution for network communication. However, their radio range is limited. Radio appliances with 25 kHz channels are characterised by moderate data rates, long range and robust modulation methods. Accordingly, they are indispensable in tactical applications. In addition to secure radiotelephony, they can be integrated in current and future data networks with IP-supported protocols such as MIL-STD-188-220 B.
Self-organizing networks with automatic routing can be realized with the MIL-STD-188-220 B, in which applications based on the IP Internet protocol are supported. Accordingly, conventional tactical radio can be expanded for the digital battle-area network, as illustrated in FIG. 1.
The combined hardware/software system 1 guarantees modern internet/intranet communication via different transmission media. The signal management and control system 2 automates radio communication on ships, while the signal management and control system 3 organises radio communication for land-based units. All of the systems 1 to 3 are incorporated in the MANET ad-hoc network 4.
Wire-bound networks and (quasi-stationary) radio networks with fast data rates, such as fixed-wireless networks, differ considerably in their properties from mobile tactical radio networks. Conventionally-used tactical radio appliances currently provide data rates up to a maximum of 16 kbit/s. The new generation of radio appliances recently launched on the market support 72 kbit/s.
Radio appliances with data rates in the order of magnitude of Mbit/s are currently under development. Commercial solutions such as WLAN provide a satisfactory solution only in special cases, because they operate exclusively at a pre-adjusted frequency. The substantial disadvantage of this solution is that it is not protected, for example, against targeted interference. In future, modern broadband-radio appliances, further disadvantages of a single-channel system are avoided by the properties described below, such as adapting the waveform to the varying channel quality.
In mobile applications, the quality and capacity of radio channels is dependent upon the topology and quality of the terrain and on the distance to be bridged.
This means that the available channel capacity can vary between the maximum data rate of a broadband radio appliance of, for example, 2 Mbit/s and that of a narrow-band radio appliance of a few kbit/s. Furthermore, the properties of the radio channels are determined by physical marginal conditions. These include, for example, attenuation, reflection, refraction, diffraction and Doppler shift.
They lead to disturbances in reception, multiple-path propagation and frequency-selective and time-variant fading. The property of the radio channel substantially affected by this is the signal quality, which is described by signal/noise ratio, signal distortion and signal jitter and, derived from these, channel capacity (data rate/bandwidth), bit error rate (BER) and range.
In certain application conditions, especially with relatively-large distances between radio nodes, radio networks can represent so-called “bottlenecks” in the networks. A plurality of measures must be investigated and realized in future networks in order to achieve a satisfactory use of the networks in spite of these temporary, potential restrictions of channel capacity and channel quality resulting from the mobility of the radio networks and their physical properties.